> Time for something completely different.
>
> My understanding, without background references is that the traditional
> justification for the virgin birth was that it was how Christ obtained a
> sinless nature. My suspicion is this related to ancient ideas on how
> conception occurred, that the man planted the seed in the woman who
> essentially provided the a suitable host. This idea of conception seems
> to have survived into the early microscope era, I recall seeing early
> drawings of sperm where people thought they could see homunculi in the
> sperm. Thus with the virgin birth, God provided the seed and mary was
> simply the cooperative recipient. Am I correct in this, or right off
> base?
>
> Now I take the Virgin Birth as a "given". In that case, in the light of
> the modern understanding of what happens at conception, how do we
> understand it, and more importantly, what is the theolological
> justification?

First, to be precise, one ought to speak of what is proclaimed in
Mt.1 & Lk.1 as virginal _conception_. One can then speak of virgin _birth_
in the sense that Mary had not had intercourse when she gave birth to Jesus,
but the term has often been taken to include the idea that Mary "retained
her virginity" in giving birth in the sense that the hymen was not broken
&c. In spite of the fact that the latter is a very traditional idea, there
is no biblical justification for it.
The Bible gives no reason for virginal conception so any statement
about its "why" is a theological deduction from scripture. The
understanding you sketch of conception, in which the male plants the seed in
the female "field", used to be common. In fact, of course, the mother
contributes to the physical (far more than the father) & genetic makeup of
the child. The idea that Jesus had to be free of original sin was one of
the reasons for the development of the idea of the Immaculate Conception of
_Mary_: She was supposedly cleansed of original sin at conception (by a
kind of retroactive application of the work of Christ) in order to be able
to conceive a "pure" child. The eastern church, with different ideas about
original sin, never needed to developed such an idea and does not accept the
Roman dogma of the Immaculate Conception.
Karl Barth (who accepted the virginal conception of Christ) argued -
I think properly - that in the Incarnation the Logos assumed _fallen_ human
nature: [To say that Christ was] "'Without sin' means that in our human and
sinful existence as a man he did not sin." Thus all attempts to figure out
how Jesus inherited some pre-fall human nature are made unnecessary.
IMO there isn't a single way to speak of the theological
significance of the virginal conception. E.g., in a letter of
Pseudo-Ignatius:
"And indeed the altogether peculiar birth of the Lord was of a
virgin alone. Not as if the lawful union were abominable, but such a kind
of birth was fitting to God. For it became the creator not to make use of
the ordinary method of generation, but of one that was singular and strange,
as being the creator."
I don't cross my fingers when I say "born of the Virgin Mary" in the
creed. But I don't think that this belief is nearly as "fundamental" as
many Christians have thought. It is not true that belief in the Incarnation
or any other critical doctrine actually requires it.